1. Field of the Invention
The present invention relates to an image projection apparatus and an image projection method for projecting an image on a projection medium.
2. Description of the Related Art
A projection apparatus that projects, by driving a display device based on an input image signal, an image according to the image signal on a screen, a wall, or the like has been known. In such a projection apparatus, there is a limit in an amount of information that can be projected due to a limit originated in a mechanism that defines a direction of projection of a projecting unit equipped in the projection apparatus, or a limit in resolution of a display device.
Therefore, a projection apparatus has been developed that performs projection of an image by reducing an information amount of an image to be projected when the resolution of an image according to an input image signal is higher than the resolution of a display device equipped in the projection apparatus.
As a first example thereof, there is a projection apparatus that reduces the resolution of an image according to an input image signal to reduce the size (area) of an image to be projected to a projectable size (area) based on the resolution of a display device, and then performs projection of the reduced image. Moreover, as a second example thereof, there is a projection apparatus that cuts out a part of region from an image according to an input image signal, and projects only an image according to the cut out region. Among projection apparatuses of the latter example, there also is one that can project a whole image according to an input image signal by, so called, scroll that sequentially changes a region to be cut out and projected, or the like.
However, in the projection apparatus of the first example described above, while a whole image according to an input image signal can be projected, there is a problem that the quality of an image displayed on a projection medium is deteriorated due to size-reduction processing of an image based on reduction of the resolution. From another point of view, it can be said that the high resolution of an input image signal is wasted by the size reduction processing of an image.
Furthermore, although the projection apparatus of the second example described above can maintain the resolution of the image signal also in an image displayed on a projection medium, there is a problem that the projection apparatus of the second example cannot project a whole image according to the input image signal at a time.
On the other hand, in Japanese Laid-open Patent Publication No. 2005-43570, a projector is disclosed that detects an orientation and a position of a main unit, extracts an actual display image to be actually displayed from an original display image based on a result of the detection, and projects the actual display image, while changing a region to be extracted as the actual display image side to side and up and down inside the original display image by moving the projector upward and downward, and rightward and leftward by a user. According to the projector of Japanese Laid-open Patent Publication No. 2005-43570, a user can appropriately project only an image of a region wished to be projected as necessary by adjusting an orientation of the main unit relative to a projection medium, or a distance to the projection medium.
However, in Japanese Laid-open Patent Publication No. 2005-43570, because the orientation of the projector is detected by, for example, imaging a display image to be projected by a charge coupled device (CCD) as an imaging device, there has been a problem that the accuracy in the orientation detection can be dependent on the contents of the display image. For example, when a dark image such as a night scene is projected in a dark room, the detection of an orientation might be disabled. Moreover, because the orientation detection is performed by analyzing an image picked up by a CCD, there has been a problem that a delay occurs in reflection of a result of the orientation detection to the display image.